Science

Infection Is a Real Pain in the Everything

¡Viva la Science!

Methicillin-resistant Staphylococcus aureus is not only terrible to say—that, of course, is why we shorten its name to MRSA and pronounce it “mer-suh,” like it’s some kind of Aquaman sidekick—but the potent, stubborn infections it creates are especially horrible. For one thing, they’re really difficult to cure. (That’s the resistant part of the name—antibiotics, our standard weapons against infection, are exactly what they’re resistant to.) For another, MRSA-caused infections, whose symptoms include everything from boils to fever, can be extremely painful.

Not so, says a new study published in Nature on Aug. 21. You’re not wracked with pain because of your body’s immune response, but because of the bacteria itself. The pain associated with MRSA isn’t your body trying to alert you to the problem; it’s actually one of the effects of the problem. "We found that major parts of the immune system are not necessary for pain during infection, but that bacteria themselves are the source of much of the pain,” says Isaac Chiu, PhD, the study's lead author.

The whole study came about because Chiu and coauthor Christian A. Von Hehn, MD, PhD, wanted to see what would happen when they cultured sensory neurons and immune cells in the same petri dish. Much to their surprise, the neurons responded to the bacteria “immediately,” says Chiu.

The study made another surprising discovery: Once pain neurons can tell that nasty invading bacteria are present, the immune system should leap into action to fight off the intruders, right? Because that's supposedly the whole point of pain neurons and an immune system and all those other intricate bits. But the scientists instead observed that the pain neurons suppressed the immune system.

It seems like a terrible idea. Something hurts! the pain neurons are apparently tweeting their friends. Let's totally not raise the alarm. Pretend everything's fine! How did it evolve that way in the first place? The question needs to be studied a lot more, but Chiu hypothesizes that our neurons might be trying to protect our body from the additional damage caused by inflammation, part of the immune system response. (Inflammation, though useful in battling infection, can cause damage to the body when it happens too often.) Those wily bacteria just might be taking advantage of a loophole.

Figuring out how pain and MRSA go hand-in-horrible-hand isn't merely an academic question. The hope is that studies like these will help doctors and scientists figure out how to deal with other serious infections and eliminate the pain that inevitably comes along with them. Let’s hope they do it soon, because ouch.